AO-AI06 458 ARMY ENGINEER DISTRICT ST LOUIS MO F/6 13/13NATIONAL DAM SAFETY PROGRAM. BRUSHY CREEK TAILINGS DAM (MO 3095--ETC(U)AUG 79 W ft BERGSTROM, F Rt BADER, M M EASTERLY

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UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE (WY.., Daeo Entoro

REPORT DOCUMENTATION PAGE READ DiSTRUC7rONSBEFORE COMPLETING FORM

I. REPORT NUMBER 12. ?OVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

4. TITLE (ind Subtitle) 5. TYPE OF REPORT & PERIOD COVERED

Phase I Dam Inspection Report

National Dam Safety Program Final F'eprt .Brushy Creek Tailings Dam (MO 30951) " R,-"mGO N.'REPORTNUMBER

Reynolds County, Missouri

.1. AUTHOR(e) S. CONTRACT OR GRANT NUMBER(a)

Corps of Engineers, St. Louis District

N/A

9. PERFORMING ORGANIZATION NAME AND ADDRESS t0. PROGRAM ELEMENT, PROJECT, TASK1, AREA &WORK UNIT NUMBERS

U.S. Army Engineer District, St. Louis ARA..O.U.T.U. R

Dam Inventory and Inspection Section, LMSED-PD . / /210 Tucker Blvd., North, St. Louis, Mo. 63101

It. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATI

U.S. Army Engineer District, St. Louis / j Augut k979Dam Inventory and Inspection Section, LMSED-PD .. '" , K- PAGES

210 Tucker Blvd., North, St. Louis, Mo. 63101 Approximately 7014. MO7 RING AGENCY NAME & ADDRESS(it different ftrom Controlllng Office) 15. SECURITY CLASS. (of this report)

National Dam Safety Program. Brushy UNCLASSIFIEDGreek Tailings Dam (Mo 30951), White ISa. DECLASSIFICATION/DOWNGRADING

!Basin, Reynolds County, Missouri. Phase / SCHEDULE

16. DISTRI I Inspection Report.

Approved for release; distribution unlimited. ,, , I-. 1 ,

A,,t,./ 417. DISTRIBUTION STATEMENT (of the abetrct antered In Block 20, !t dlterent from Report)

IS. SUPPLEMENTARY NOTES

I. KEY WORDS (Continue on reveree aide if necesary and Identify by block number)

Dam Safety, Lake, Dam Inspection, Private Dams

24 ABS?"RACT (Come -am eveW 8b N n&C-eaty 411 Identify by block numbe)

This report was prepared under the National Program of Inspection ofNon-Federal Dams. This report assesses the general condition of the dam withrespect to safety, based on available data and on visual inspection, todetermine if the dam poses hazards to human life or property.

DOR W 43 EDITON OF I NOV GS IS OBSOLETE (//UCASFE, m 473 o oRyssooet. UNCLASSIFIED

SECURITY CLASS1FICATION OF THIS PAGE (Whe, Data Enteed)

-. a .

EcumriY CLAMPICAfICOIO T141S PA0GE(U- DO- E.We40-

SIECUpqITy CL.ASSIFICATION OF THIS PAGE(F?'.I DON, Enter

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WHITE BASIN

BRUSHY CREEK TAILINGS DAM

REYNOLDS COUNTY, MISSOURI

MO 30951

PHASE 1 INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

United States ArmyCorps of Engineers... Serving the Army

0 ... Serving the Nation

St. Louis District

FOR: STATE OF MISSOURI

AUGUST 1979

14 1

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

BRUSHY CREEK TAILINGS DAM - MO. 30951

TABLE OF CONTENTS

Paragraph No. Title Page No.

1.1 General 1

1.2 Description of Project 1

1.3 Pertinent Data 2

SECTION II - ENGINEERING DATA

2.1 Design 5

2.2 Construction 5

2.3 Operation 6

2.4 Evaluation 7

SECTION III - VISUAL INSPECTION

3.1 Findings 8

3.2 Evaluation 11

SECTION IV - OPERATIONAL PROCEDURES

4.1 Procedures 13

4.2 Maintenance of Dam 13

4.3 Maintenance of Operating Facilities 13

4.4 Description of Any Warning System in Effect 13

4.5 Evaluation 13

SECTION V - HYDRAULIC/HYDROLOGIC

5.1 Evaluation of Features 15

SECTION VI - STRUCTURAL STABILITY

6.1 Evaluation of Structural Stability 18

SECTION VII - ASSESSMENT/REMEDIAL MEASURES

7.1 Dam Assessment 20

7.2 Remedial Measures 20

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LIST OF PLATES

Plate No. Title

1. Location Map2. Vicinity Topography3. Brushy Creek Tailings Pond4. Brushy Creek Tailings Dam - Plan5. Brushy Creek Tailings Dam - Cross Section6. Brushy Creek Tailings Dam - Dam Profile7. Brushy Creek Tailings Dam - Photo Index

APPENDIX

A - Hydrologic Computations

B - Engineering Data and Plates Furnished by Owner

LIST OF PHOTOGRAPHS

Photo No. Title

1. Downstream Slope at Uncompleted Portion of Embankment2. Downstream Slope from Embankment Crest3. Downstream Slope Looking Toward Southeast Abutment4. Upstream Slope During Deposition of Unsegregated

Tailings5. Upstream Slope With Scarp Created by Erosion Due to

Hydraulic Method of Tailings Deposition6. Upstream Slope and Tailings Impoundment7. Upstream Slope at Uncompleted Portion of Embankment8. Spillway Looking Downstream

AccessianFoOTIS GRA&IDTIC TAB 0Unannounoed3ustifi~i

By- -

Distributi on/ ..

I Availbilit? Codes-!Av: ." and/or

n Dist Special

.....-

PHASE I REPORT

NATIONAL DAM SAFETY PROGRAM

Name of Dam: Brushy Creek Tailings DamState Located: MissouriCounty Located: Reynolds County

(Mark Twain National Forest)Stream: Schoolhouse Branch of Bill's CreekDate of Inspection: 15 November 1978

Brushy Creek Tailings Dam, inventory number MO 30951, wasinspected.' ~in the "Recommended Guidelines for Safety Inspection ofDams." Tiesenguidelines were developed by the Chief of Engineers,U.S. Ari, Washington, D.C., with the help of Federal and stateagencites, professional engineering organizations, and privateengineers. The resulting guidelines are considered to represent aconsensus of the engineering profession.

Based on the criteria in the guidelines, the dam is in the highhazard potential classification, which means that loss of life andappreciable property loss could occur in the event of failure of thedam. It is classified in the large size category due to its120-foot height.

Our inspection and evaluation indicates that the spillway doesnot meet the criteria set forth in the guidelines for a darn havingthe above size and hazard potential. The guidelines recommend thatthe spillway be capable of safely handling the Probable MaximumFlood (PMF). A hydraulic/hydrologic analysis of this dam andreservoir indicates that any flood exceeding 55 percent of the PMFwill result in excessive spillway erosion with the essential effectof overtopping the dam. A flood with a 1 percent chance ofoccurrence in any year (once in 100 years on the average) will becontained within the tailings reservoir without any spillwayoverflow.

A sudden breach of this dam could be expected to cause propertydamage and serious hazard to human life for a distance ofapproximately 30 miles downstream of the dam. Within this reach arenumerous structures, the communities of West Fork and Centerville, acampground, and Missouri Highway #21. Included therein are portionsof Bill's Creek, and the West Fork of the Black River.,_

Other deficiencies noted are: (1) uncontrolled surface erosionon the upstream embankment slope and at the southeast abutmentinterface with the downstream slope and (2) underdrainage filtersnot constructed according to currently accepted standards toproperly prevent internal erosion through the underdrainage system.These deficiencies should be corrected under the direction of an

engineer experienced in the design and construction of dams. Also,the lack of stability and seepage analyses on record, especiallyseismic and liquefaction studies considering the nature of theembankment materials and construction methods, is a deficiency whichshould be corrected.

The above deficiencies, while important, are not considered tocritically endanger the subject structure. Hence, Brushy CreekTailings Dam is classified as possessing minor deficiencies.

WAYIZ R. BERGSTROM

Soils Engineer

St. Louis DistrictCorps of Engineers

FREDERICK R. BADER, P.E.Hydraulic EngineerSt. Louis DistrictCorps of Engineers

I

MICHAFL 1. EASTERLYGeologistSt. Louis DistrictCorps of Engineers

SIGNED 12 SEP,,Submitted By SG E iChief, Engineering Division

Date

SIGNED _______ ,Approved By SIGNED

Colonel, CE, District Engineer Date

I. - i

L A

Overview of Brushy Creek Tailings Dam Looking From Southeast Abutment.

* XI

PHASE I INSPECTION REPORTNATIONAL DAM SAFETY PROGRAM

BRUSHY CREEK TAILINGS DAM - ID NO. 30951

SECTION I - PROJECT INFORMATION

1.1 GENERAL.

a. Authority. The National Dam Inspection Act, Public Law92-367, authorized the Secretary of the Army, through the Corps ofEngineers, to initiate a program of safety inspection of damsthroughout the United States. Pursuant to the above, the DistrictEngineer, St. Louis District, Corps of Engineers, directed that asafety inspection of the Brushy Creek Tailings Dam be made.

b. Purpose of Inspection. The purpose of the inspection wasto make an assessment of the general condition of the dam withrespect to safety, based upon available data and visual inspection,in order to determine if the dam poses hazards to human life orproperty.

0. Evaluation Criteria. Criteria used to evaluate the damwere furnished by the Department of the Army, Office of the Chief ofEngineers, in "Recommended Guidelines for Safety Inspection ofDams." These guidelines were developed with the help of severalFederal agencies and many state agencies, professional engineeringorganizations, and private engineers.

1.2 DESCRIPTION OF PROJECT

a. Description of Dam and Appurtenances.

(1) The dam is constructed of lead mine tailings, a sandymaterial similar to ground agricultural limestone, over a crushedrock underdrainage system and earth starter dam. The configurationof the dam, reservoir, and appurtenant structures are best describedby the drawings and photos attached herewith. See Plates 1 through6.

(2) Pertinent physical dimensions and numerical data arelisted in paragraph 1.3 below.

b. Location. Northwest corner of Reynolds County, Missouri,further described as Sections 22 and 23, Township 33 North, Range 2West.

c. Size and Classification. Large

d. Hazard Classification. High

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e. Ownership. St. Joe Minerals Corporation, Viburnum,

Missouri 65566

f. Purpose of Dam. Lead mine waste retention.

g. Design and Construction Hirtory. The dam was designed bythe owner and an earthen starter dam was started in 1971.Thereafter, the dam was constructed incrementally by hydraulicdeposition of sand-sized tailings separated by cyclones from thefiner portion of the tailings slurry. Presently, the dam remains

under construction and is expected to reach the final configuration

(Plate B-5) in the early 1980's. Approximately 4500 tons per day

(5-day week) of tailings slurry are deposited on the upstream slope

of the dam and in the reservoir. See Section 2.2 for more detailedexplanation.

h. Normal Operating Procedures. Inflows to the reservoir

occur from: (1) normal runoff from the watershed and (2) dtposition

of tailings slurry. The reservoir storage is regui~ted by:(1) surface evaporation and (2) seepage through the dam

underdrainage system into the downstream reclamation pond,

subsequently to be returned by pumping to the upstream mill water

reservoir. This is essentially a closed hydraulic system and no

releases of mill water or mine tailings are expected. Anuncontrolled spillway is provided for potential outflows from thereservoir.

1.3 PERTINENT DATA

a. Drainage Area.

Tributary to Brushy Creek Mill Dam (#30161) - 93 acres

Local runoff tributary to Brushy Creek Tailings Dam

(#30951) - 546 acresTotal area tributary to Brushy Creek Tailings Dam (#30951) -

639 acres

b. Discharge at Damsite.

(1) Maximum known flood at damsite - Unknown

(2) Spillway capacity - see section 5.1(d)

(3) Seepage through underdrainage systern - 75-100 gallons

per minute

c. Elevation. Feet above mean sea level (msl) based upon

assumed benchmark and/or USGS topographic map.

(1) Minimum top of dam - 1140

2

r£

(2) Maximum top of dam - 1203

(3) Spillway crest - 1125.

(4) Streambed at centerline below dam - 1020.0

(5) Observed pool elevation - 1110+

(6) Maximum tailwater - Unknown

d. Reservoir. Length of maximum pool - 4200+ fte. Estimated Storage. (Acre-ft of water and/or submerged

tailings)

Pool Elevation Corresponding Storage

1020 01100 14601125 3250 Spillway crest1140 4790 Top of dam (min)1160 7500

f. Reservoir Surface Area. (Acres)

(1) Observed pool - 68.5

(2) Spillway crest - 91.0

(3) Top of dam - 116.0

g. Dam.

(1) Type - Lead mine tailings embankment placedhydraulically.

(2) Length - 1200 ft +

(3) Height - 120 ft (minimum)

(4) Top Width - 12 ft (minimum)

(5) Side Slopes:

(a) Downstream - 1V (Vertical) to 3.5H (Horizontal)

(b) Upstream - 1V to 4H

3

(6) Zoning - Original earthen starter dam has been coveredby fine, sand-sized tailings both upstream and downstream.

(7) Impervious Core - Earthen starter dam as noted above.

(8) Cutoff - Compacted clayey earth trench was carried 8to 10 feet deep to rock and extended up valley wails toapproximately elevation 1050.

(9) Drainage Provisions - Crushed rock underdrain withsteel outlet pipe and settling basin.

(10) Grout Curtain - None

h. Diversions. None at present.

i. Spillway.

(1) Type - Unregulated open channel ditch excavated innatural soil. Also functions as interception ditch for hillsiderunoff.

(2) Bottom Width - 10 ft +

(3) Depth - Varies

(4~) Side Slopes - 1V on 1H typically

(5) Bottom Slope - Varies

(6) Length - 1200 ft +

(7) Inlet - See Photo 7

(8) Outlet - See Photo 1

.J. Emergency Spillway. None

k. Regulating Outlets. None - Some uncontrolled seepagethrough underdrainage system. Estimated at 75 gpm on day ofinspection.

SECTION II - ENGINEERING DATA

2.1 DESIGN.

No design analyses are available.

2.2 CONSTRUCTION.

The initial earthen embankment was reportedly constructed in1971-72 by AG Construction Company, of Perryville, Missouri. Afterthe clearing of vegetation in the dam foundation area, a keyway wasexcavated across the valley. This key trench was excavated 8 to 10feet to the top of rock and was carried up the valley walls toapproximately elevation 1050.

The earthen dam was then constructed over the keyway. Clayeyborrow was obtained from the overburden near the northwest (right)abutment and downstream of the starter dam. Specifications used bythe mining company required 12-inch maximum lifts with materialdensities no less than 95 percent of optimum. Reportedly, asheepsfoot roller was utilized for compaction. Slopes were 1V on2.5H upstream and 1V on 2H1 downstream.

During construction of the earthen dam, natural streamfiow wasdiverted through a 211-inch diameter, Schedule 10, steel pipe. Thispipe extended through the earthen embankment approximately at thelocation of the streambed. This pipe was specified to have a steelplate collar, 4 feet by 6 feet by 1/2 inch, at the dam centerline.Additionally, all joints were to be properly welded. This pipedischarged into a ditch behind a smaller dam, creating a settlingbasin. These features are presently entirely buried beneath thedownstream slope of the main embankment. These features can be seenin Plates B-i and B-2.

In June 1973, the first pass was made across the dam crest witha mobile cyclone rig which separated the coarser sand-sized tailingsfrom the remainder of the waste slurry. These sands were depositedhydraulically in a single lift raising the dam crest from elevation1053 to 1080. The spillway was raised up the northwest abutmentfrom the original earthen dam emergency spillway elevation of 10148to elevation 1060. This can be seen in Plate B-1. This pass wascompleted in October 1973.

The second pass commenced in October 1973 and was completed inJuly 1974. It raised the embankment crest to elevation 1110 with anew spillway at elevation 1094. A ridge was constructed upstreamalong the spillway at this elevation.

5

The third and final pass began in July 1974 and continued untilit was temporarily halted in 1978. The cyclones are currently beingutilized elsewhere and the completed dam section is not expecteduntil at least late 1982. The present spillway elevation is 1125and the planned elevation of the completed dam section isapproximately 1185.

Throughout the construction period, the cyclone overflow (thefine material suspended in slurry form) has been depositedhydraulically over the upstream face of the dam.

A seepage reclamation pond was placed downstream of the damtoe. It is reportedly excavated to rock, approximately 10 feet fromthe natural ground surface. It is shown in Plate B-i.

During construction, the right toe area experienced overflow ofthe sand embankment material into the reclamation pond. A rock toewas added at that time with a drain pipe from the toe area leadinginto the pond. A limited portion of the toe area subsequentlywashed out once but was repaired and the material removed from thepond.

During the summer of 1978, an internal erosion feature appearedon the surface of the third and final pass. It was reportedly 2/3of the dam height up the downstream slope and left of the valleycenterline (looking downstream). It has been described as a 2-footdiameter, chimney-like vertical hole with a negligible depressioncone at the surface. It was repaired by dropping straw into thehole and backfilling with embankment sand. No embankment materialwas noticed in the seepage water from the downstream drain pipe. Itshould be noted that a similar feature has developed more than onceat a nearby facility constructed in a similar manner.

No flow through the present spillway has reportedly occurred.No slides, overtopping, or seepage problems are reported to haveoccurred.

2.3 OPERATION.

Runoff in excess of the needed volume of water reclaimed fromthe upstream portion of the reservoir must pass over theuncontrolled spillway if not stored. Flow in this spillway has notoccurred. No operating records for the various inflow and outflowpumps are available.

A number of open-system piezometers have been installed andregularly monitored in the embankment. A summary of the observedpiezometric readings is shown on Plate B-3.

6

Also shown in Appendix B (Plate B-4l) are the results ofgradation tests performed on samples of the embankment sand, thecyclone overflow, and unsegregated tailings materials. These testswere performed, in part, by St. Joe Minerals Corporation and also bythe U.S. Bureau of Mines, under the direction of Mr. R. L. Soderbergof the latter agency.

Company personnel have indicated that the seepage drain at thedam toe discharges up to approximately 75-100 gpm. The pumps in thereclaim pipeline average approximately 75 gpm but do not operatecontinuously. They are operated by float-tripped switches when thepond depth exceeds approximately 3 feet. Company analyses haveindicated that the water in the seepage reclamation pond is verysimilar to the mill process water entering the main reservoir butcontains a little more iron. Only once has the company removedaccumulated sediment from the seepage reclamation pond. The removalwas required by the previously noted toe surface erosion into thepond.

Future plans include constructing dams at the upper end of thevalley and in two side hollows, completion of the existing mainembankment, construction of a permanent spillway, completion ofvalley filling, and conversion of the reservoir to waterdecantation. None of these plans are addressed hergin but aredepicted in part on Plate B-5.

2.14 EVALUATION.

a. Availability. The preceding construction and operationinformation was cooperatively provl.ded by Mr. John E. Kennedy,Director of Environmental Control, St. Joe Minerals Corporation.

b. Adequacy. The information presented above, in combinationwith the field survey and visual inspection, is considered adequateto support the conclusions of this report. However, the fact thatno seepage and stability analyses comparable to the requirements ofthe guidelines are on record is a deficiency which should berectified.

c. Validity. No conclusions can be drawn concerning thevalidity of original design analyses as none are known to exist.

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SECTION III - VISUAL INSPECTION

3.1 FINDINGS.

a. General. The dam and reservoir are located in a sparsely

populated, generally forested area. The topography is generally

rolling and locally rough.

b. Project Geology. The Brushy Creek Tailings Dam is located

in the Salem Plateau Section of the Ozark Plateau Physiographic

Province, an area which is underlain by horizontally bedded lower

Paleozoic rocks deposited on the western flank of the Ozark Uplift.

Metallic ore bodies occur locally in the lowermost Cambrian units

due to the proximity of this major structural feature.

The lower slopes and valley floor at the damsite are underlain

by the Ordivician Gasconade formation, a fine to coarse crystalline,

cherty dolomite with a dolomitic quartz sandstone basal unit. A

boring drilled in the valley near the dam axis showed a combined

thickness of 593 feet of Gasconade, Eminence, Potosi, and

Derby-Doerun dolomite formations below the center of the dam. The

Derby-Doerun formation is underlain by a 157-foot thickness of the

Davis Shale formation, followed by 300 to 400 feet of lower Cambrian

dolomite and sandstone above the pre-Cambrian basement.

The bedrock surrounding the damsite is well blanketed by 10 to

20 feet of residual soil. Consequently, no outcrops were visible

and the jointing and weathering characteristics of the rock could

not be observed. The residuum is composed of reddish brown clay

with abundant porcelainous and banded chert fragments of all sizes

and small amounts of oolitic chert and fine-grained sandstone. The

spillway excavation on the right abutment revealed irregular

horizontal beds of chert and very highly weathered dolomite withinfive feet of the ground surface.

No springs, sinks, or caves were observed or reported in the

reservoir area. A wet weather seep is reported to have existed

prior to construction on the right abutment near the dam axis.

Boreholes had been drilled in the impoundment area before the dam

was constructed but were plugged to prevent water seepage into mine

workings.

No evidence of faulting was observed at the damsite. No

expansive clays or shales were observed or known to occur there.

Some slope failures had occurred in steep (approximately 1:1.5) road

cuts approximately 50 feet high in residuum close to the site.

However, no similar cuts have been made in the reservoir area.

8

Lead and small amounts of copper and zinc are currently beingrecovered from a narrow, north-south trending ore body in the lowerCambrian Bonneterre dolomite formation at a depth of approximately1000 feet below the extreme upper end of the reservoir. The mineworkings have penetrated to the limits of the ore body in this areaand are not expected to extend further under the impoundment. Thereservoir area has been thoroughly explored and no other mineralresources have been discovered.

c. Dam. As explained in Section 2.2, the full dam section hasnot been completed at the northwest (right) abutment. Surfaceerosion, apparently caused by hydraulic material deposition, isevident at the uncompleted portion of the embankment. See Photo 1.

The downstream slope of the dam is typically 1 vertical on 3.5horizontal. It has few discontinuities and little surface erosion.See Photos 2 and 3. There is no evidence of movement nor is thereany vegetation or slope protection.

Where the downstream slope interfaces with the southeastabutment there is an erosion channel. This surface erosion isentirely in the sand tailings material and ranges up to 3 feet deepwith a width of 14 to 5 feet. A diversion ditch has been provided innatural overburden materials on the abutment in order to alleviatethis problem by preventing abutment runoff from reaching theembankment slope. Approximately one third of the dam height fromthe toe, nearly 25 trees, 14 to 114 inches in diameter, were notcleared prior to tailings disposal. These trees are partiallycovered by tailings on the southeast abutment interface. See Photo3. A similar situation exists at approximately two-thirds of thedam height from the toe.

As seen in the overview photograph, there is a discontinuity onthe crest at the southeast abutment. It consists of a benched areaapproximately 80 feet by 30 feet and about 8 feet from the damcrest. It apparently is a result of previous construction effortsand is not a significant feature except as a source of runoffconcentration and, therefore, erosion.

The upstream slope is more variable than the downstream slope.As seen in Plate 5, the slope is generally near 1V on 4H. However,it is locally steeper. Wind erosion is evident by the formation ofa bulging drift on the upstream side of the embankment crest. Thisdrift has resulted from winds blowing from the downstream portion ofthe valley. Photos 4 and 5 show the undercutting and vertical scarpformations which occur on the upstream slope due to materialdeposition in fluid form. This has occurred at several locationsacross the length of the dam. Southeast of the valley centerlinethere is an erosion channel from the crest upstream to the reservoir

9

surface. Toward the upstream end of the channel, it is up to 15feet deep and 20 feet wide. It is reportedly due to accidentaldischarge from a break in the transporting pipe on the embankmentcrest. There is a depression near the valley centerline atapproximately elevation 1150 in the upstream slope. It is 80 feetby 40 feet and is up to 6 feet deep on the downstream side. Thereis no apparent reason for its formation.

There is no slope protection on either the upstream ordownstream slopes. Company personnel have indicated that efforts toprevent surface erosion at another mine location by placement of aclay layer only served to aggravate erosion by concentratingrunoff. Current efforts at establishing vegetative cover have metwith very limited success at the other mine location. Photo 6 showsthat there is some construction debris remaining on the upstCreamslope.

d. Appurtenant Structures. The appurtenant structures forthis dam essentially consist of: (1) an open-channel, unlinedspillway cut into the northwest abutment, (2) an upstream eam andreservoir for use as millwater supply, and (3) a downstreamcollection system for seepage through and beneath the dam. Ofthese, only the first will be examined In this section. The lattertwo will be examined in succeeding paragraphs.

The spillway location has changed several times during theconstruction of the embankment. Its present location can be seen inPlate 3. It is viewed from the embankment crest in Photos 1 and 7.The spillway has been cut into the overburden material on thenorthwest valley wall. Both banks are formed by virgin material ascan be seen in Photo 8. It is a gravelly, plastic clay thatexhibits rainfall runoff erosion. There is no evidence ofsignificant spillway flow. The clay material has a fissuredstructure with rootlets in many of the fracture separations. Thereis a cleared slope located above the spillway in the northwestabutment. The spillway discharges near the downstream portion ofthe northwest abutment.

e. Reservoir Area. During inspection, unsegregated tailingsdirect from the milling operation were being deposited in thereservoir (see Photo 4). These tailings then flowed on a gentleslope up-valley where the suspended tailings dropped out of theslurry material. This deposition method causes erosion at theupstream face of the dam where an undefined transition from finematerial to embankment sands results (see Photo 5). After draining,the reservoir materials can support walking but are very easilyliquified. Clarified water was evident in the upstream portions ofthe reservoir. The discharging slurry was noticeably warm resultingin reservoir temperatures warmer than the ambient air temperature.

10

A small reservoir Is maintained in an upstream tributary valleyas a mill water source. Clarified water from the several sources ispumped into this reservoir to help maintain an adequate watersupply. The hydrologic impact of this reservoir upon the tailingspond is examined in Section 5.

f. Downstream Channel. Immediately downstream of the rockfilltoe is a seepage collection and reclamation pond (see Photo 2).Erosion of tailings through the rock toe was evident. Reportedly,this had occurred during embankment deposition. There was an 8-inchdiameter steel pipe beneath the rock toe which dischargedapproximately 75 to 100 gpm into the seepage reclamation pond. Thispipe reportedly collects seepage from the crushed rock interiordrains. The toe area near the pipe drain was somewhat wet,especially at the erosion channel in the rockfill toe.

The discharging water from the drain pipe was clear andpossessed a temperature similar to that of' the reservoir water. Theseepage reclamation pond water was of a similar temperature butsomewhat discolored. Its yellowish color was similar to the colorof surface runoff water in the downstream valley area.

The downstrear right toe area Is somewhat flat. An 8-inchdiameter steel pipe leads from this area into the pond. It was notdischarging.

Downstream of the seepage reclamation pond, surface runoff fromrecent rainfall was evident. However, no surface evidence ofexcessive groundwater pressures or erosion due to seepage exit wasapparent. No springs immediately downstream of the dam could befound.

3.2 EVALUATION.

Potential erosion within, and downstream of, the unlinedspillway in the event of significant spillway discharge constitutesa serious hazard. Degradation caused by encroachment of thispotential erosion into the embankment sand fill could be very rapidand must be prevented. Erosion protection in the spillway anddischarge area should be provided. Additionally, the stability ofthe abutment slope above the spillway cannot be assured. Astability analysis of this slope should be performed by aprofessional engineer with due consideration given to potentialerosion at the slope toe.

Surface erosion features should be inspected and repaired on aregular basis. The erosion gully in the upstream embankment slopeand especially those at the abutment contacts are potentiallytroublesome and should be repaired.

As noted in Section 3.1.e., the hydraulic method of tailingsdeposition causes severe erosion on the upstream dam face (Photo 5).Efforts to minimize this erosion should be implemented.Additionally, sufficient freeboard between the reservoir watersurface and the fine tailings deposition area (See Plate 3) shouldbe maintained to prevent a free pool surface from resting againstthe upstream dam slope. Without such a precaution, wave erosion mayresult and the embankment seepage conditions would be alteredsignificantly.

The depression in the upstream embankment slope, noted inSection 3.1.c., should be monitored on a regular basis for anychanges in its siz^ or depth. While possibly a result ofconstruction efforts, it may also signify potential interior erosionas discussed in Section 6.1.b.

12

SECTION IV -OPERATIONAL PROCEDURES

~4.1 PROCEDURES.

Reservoir regulation is performed principally by evaporationand by pumps which remove reservoir water for reuse in the mill.The mine waste, consisting of tailings in a suspended slurry form,is deposited near the upstream face of the dam and allowed to runup-valley. The suspended materials drop out of the slurry as theflow velocity is reduced. In the upper reaches of the reservoir, apond of somewhat clarified water remains. Here it is pumped to thesmall upstream mill supply reservoir to be reused. Note also thatwater from the downstream seepage collection pond is regularlypumped back into the main reservoir.

4.2 MAINTENANCE OF THE DAN.

There is no formal maintenance and inspection program.However, there are reportedly company personnel on the damsitedaily. Small bulldozers are used to fill erosion gullies at the damabutment interfaces when necessary. Additionally, remedial effortswere directed toward correction of the "chimney"-1ike erosionfeature discussed in Section 2.

4.3 MAINTENANCE OF OPERATING FACILITIES.

No regular maintenance program for the uncontrolled, unlinedspillway exists. Pumps and associated pipelines utilized in seepagereclamation, tailings disposal, and clarified water reuse aremaintained as necessary for continued operation.

4.4 DESCRIPTION OF ANY WARNING SYSTEM IN EFFECT.

No downstream warning system is known to exist. However, thereclaim pumps provide a warning to personnel if they becomeinoperative.

4.5 EVALUATION.

Recommended remedial efforts on the dam and spillway arediscussed in Sections 3 and 7. Future maintenance on a regularbasis to prevent erosion is recommended. Encroachment of largevegetation (bushes and trees) in the spillway and on the dam shouldbe prevented as well as any animal burrows. Regular monitoring orall piezometers and analysis of the data with respect to stabilityand seepage as noted in Section 6 are recommended. Seepage flowsshould be closely monitored for changes in volume/rate, amount oftransported sediment, and water quality characteristics.

13

It should be noted that future changes in operating procedures,including but not limited to abandonment of the reservoir as anoperating waste disposal facility, cannnot be addressed herein.Such changes will have to be carefully evaluated on an individualbasis and together as a whole to determine their impact on thesafety of the dam and re3ervoir.

14

LA

V

SECTION V - HYDRAULIC/HYDROLOGIC

5.1 EVALUATION OF FEATURES

a. Design Data. No hydrologic or hydraulic design informationwas available for evaluation of these reservoirs and dams; however,significant dimensions of the dams and spillways were based upondesign information furnished by the owner. Other dimensions of thedam and reservoir were measured and/or surveyed on the date ofinspection or estimated from topographic mapping. The map used inthe analysis is the 7-1/2 minute US Geological Survey quadranglesheet for Greeley, Missouri, dated 1967. The channel of the westfork of the Black River in the hazard reach of the dam is shown onthe 7-1/2 minutes quadrangle sheets for Corridon, Centerville, andLesterville. These maps are dated 1967 and 1968. Surface soilinformation has not been mapped using modern soil mappingtechniques, however, older information and data from nearby areasindicate that the surface soil of the upland watershed above the damis primarily Clarksville stoney loam. This soil has been classifiedas belonging to hydrologic soil Group "B," a soil with a moderaterate of moisture transmission.

b. Experience Data. No recorded rainfall, runoff, discharge,or pool stage data was available for this reservoir or watershed.

0. Visual Observation.

(1) Watershed - The watershed is forested with mixedhardwoods and softwoods predominately of oak, hickory, pine, andcedar varieties. The area of the reservoir pool surface isapproximately 10 percent of the total watershed area.

(2) Upper Reservoir - A portion of the drainage area abovethe main tailings dam is controlled by a dam and reservoir for thepurposes of storing mill process water for the mining operation.This dam is basically of earthfill construction with a double1 8-inch diameter corrugated metal pipe spillway supplemented by a4-foot wide by 5-foot high box culvert. Water is supplied to themill dam by natural runoff from 93 acres and by pumping from thereclamation pond below the main dam, and is withdrawn for use in thelead mining process. As a result of the overtopping analysis,further described in Section 5-1.d, the mill dam was determined tobe capable of passing a storm of 100 percent of the Probable MaximumFlood and is otherwise not considered to significantly affect theevaluation of the primary tailings dam. This dam is furtherclassified as being of intermediate height (85 ft.) and storagecapacity (630 Ac-ft.).

15

(3) Tailings Reservoir - The reservoir upstream of thetailings dam is best described by maps and photographs inclosedherewith. The reservoir is partially filled by fine sand andsilt-sized tailings material and the proportion of water to minetailings cannot be determined. The extent of tailing deposition isnot expected to have significant effect on the hydrauliccharacteristics of the reservoir. The level of tailings storage, asobserved during the dam inspection, was approximately 15 feet belowthe crest of the spillway located at the north end of the damF embankment. Photographs and field observations reveal theunprotected tailings material of the embankment to be highlysusceptable to rapid erosion by concentrated surface flows orpossibly by very intense rainfall. It was observed that somedifficulty has been experienced due to hillside surface runoffcausing gullies at the interface of the hillside and theembankment. A diversion ditch in native soils on the south end andthe "spillway" on the north end have been provided to allevia'e thisproblem.

(24) Spillway - The "spillway" at the north end of the damembankment is constructed in native undisturbed soils at a pointjust beyond the embankment. No erosion protection of rock,concrete, or vegetation is provided for this spillway. The geometryof spillway cross sections is best described by Photo No. 8. Thevertical profile of the spillway is approximately parabolic, concavedownward. The principal effect of this profile is a very steepchannel slope near the spillway outlet, a condition which couldcause erosion should significant discharge occur.

(5) Seepage - The magnitude of seepage through this dam isnot hydrologically significant to the overtopping potential.

d. Overtopping Potential. One of the primary considerationsin the evaluation of the safety of the Brushy Creek Tailings Dam isassessment of the potential for overtopping and consequent failureby erosion of the embankment. Since the "spillway" of this dam iscomposed of erodible materials, the potential consequences ofsignificant spillway discharges are substantially the same as theovertopping of the dam embankment. Hydraulic considerations of thematerial erodibility and of the spillway geometry suggest that flowsbelow a velocity of 5 feet per second or a discharge of 50 cubicfeet per second will not result in substantial spillway erosion.For the purpose of determining the overtopping potential of thisdam, spillway discharge of greater than 50 cubic feet per second isconsidered to produce the effects of overtopping.

Hydrologic analysis of the tailings dam using the data and method asinclosed and described in Appendix A, "Hydrologic Computation,"indicate that a flood of greater than 55 percent of the Probable

16

Maximum Flood (PMF) will effectively overtop the dam. The PM? isdef'ined as the flood event that may be expected to occur from themost severe combination of critical meteorologic and hydrologicconditions that are reasonably possible in the region. This dam isclassified by the guidelines as one of large height and intermediatestorage capacity. The guidelines recommend that a dam of this sizeand hazard potential (high) be capable of safely passing the outflowof the Probable Maximum Flood. The following overtopping data werecomputed for the tailings dam, assuming no erosion of the spillwayor embankment.

Maximum Pool Maximum SpillwayElevation Spillway Depth Discharge

Percent PM? Cmsl) (feet) (cu. ft. per sec.)

50 1125.8 0.3 655 1126.6 1.3 30

100 1136.1 10.8 990

A flood with 1 percent chance of occurrence in any year (once in 100years on the average) will be contained within the tailingsreservoir without any spillway overflow.

The tailings dam is classified as one of high hazard potential sincefailure of Brushy Creek Tailings Dam could result in substantialhazard to human life and flood damage to the mouth of the west forkof the Black River near Lesterville, located approximately 30 streammiles below the dam. Large amounts of sediment, debris, andtailings from the dam and impoundment could be expected to bedeposited in the stream and floodplain for a large proportion ofthis distance. Fine sediment and washload would be carried anddeposited considerably further. Within this reach of Bill's Creekand the west fork of the Black River are numerous structures, thecommunity of West Fork (approximately 4-1/2 miles below the dam),Cook's Cave (13-1/2 miles), Sutton Bluff Campground (15 miles),Missouri Highway #21 (19 miles), and the city of Centerville (20miles). The west fork is considered navigable by canoeists belowCenterville during periods of high water.

17

,. . .,

SECTION VI - STRUCTURAL STABILITY

6.1 EVALUATION OF STRUCTURAL STABILITY.

a. Visual Observations. Visual observations which adverselyaffect the structural stability of this damn are discussed inSection 3.

b. Design and Construction Data. Design data are unavailable* but the construction history is described in Section 2.

The fine granular materials utilized in constructing themajority of the embankment should be highly susceptible to internalerosion. Plate B-4l shows the range of gradations determined fromsamples obtained from the cyclone underflow (sand-sized materialsused in the embankment). Unsegregated tailings and cyclone overflow(fines) are also shown on Plate B-4. The rockf ill drains,consisting of rock sizes greater than 6 inches in diameter, do notconform to acceptable standards for graded filters in fine sands.The potential for internal erosion cannot, therefore, be excluded.

The "chimney-like" erosional feature described in Section 2demonstrates the potential for internal erosion. The use of strawin backfilling this feature cannot be considered to provide apermanent solution. Additionally, the tendency for the embankmentsand to form weak bonds (either through capillarity or weakcementation) and stand vertically (see Photo 1) demonstrates thatthe embankment sand does not readily self-seal existing erosionfeatures. Strong cementation within the sand could reduce itserosion susceptibility but was not evident at the site.

Contributing to the potential for internal erosion are the twopipes located within the structure. The plug on the downstream endof the 24-inch pipe that passes beneath the earthen starter dam, ifdefective, may subject the crushed stone drains to unduly largeheads. Additionally, the 8-inch drain pipe that discharges into theseepage reclamation pond has no graded filters at its entrance.Such filters, provided according to currently acceptable standards,minimize the potential for internal erosion to occur at the pipeentrance.

Based upon information concerning the method of constructingthe key trench, the effectiveness of the impervious cutoff at thebedrock surface is not certain. Seepage at this interface may alsocause internal erosion.

Since the seepage reclamation pond has only been cleaned outonce as a result of the surface erosion noted in Section 2, thevolume of internally eroded material has apparently been minimal todate.

18

Surface erosion features at the abutment interfaces areevident. Careful observation of these interfaces is required. Noimpervious core and trench are carried above approximately elevation1050, increasing the potential for internal seepage at theseinterfaces.

The centerline method of construction, utilized on thisstructure, results in an ill-defined transition between theembankment sand material and the fine material in the reservoir.However, the grain size analyses, shown in Plate B-4l, demonstratethat there is indeed a transition to finer materials upstream of theembankment face. This provides a natural upstream filter system andreduces the likelihood of an uncontrolled phreatic surface locatedhigh in the main embankment. The piezometer data, summarized inPlate B-3, indicate the range of phreatic surface experienced in theembankment to date. They do not indicate the presence ofsignificant abnormalities in overall seepage characteristics.

c. Operating Records. No operating records, apart from thepiezometric data, are available.

d. Post Construction Changes. No significantpost-construction changes have occurred.

e. Seismic Stability. The dam is located in Seismic Zone 2,as shown in the inspection guidelines. Since neither originaldesign analyses nor properties of the construction materials areavailable, an accurate seismic analysis cannot be made. Therelatively flat slopes reduce the likelihood of slope and foundationinstability in the event of seismic loadings. However, the sand andsilt-sized tailings material, deposited hydraulically, is expectedto be susceptible to liquefaction. Failure of the embankment as aconsequence of potential liquefaction cannot be excluded. Thepotential for such an occurrence should be thoroughly investigatedby a professional engineer experienced in the design andconstruction of dams.

19

SECTION VII -ASSESSMENT/REMEDIAL MEASURES

7. 1 DAM ASSESSMENT.

a. Safety. Several deficiencies exist which should becorrected. These include: spillway inadequacy due to insufficienterosion protection therein, uncontrolled surface erosion on theupstream embankment slope and at the southeast abutment interface,and underdrainage filter provisions not constructed to currentlyacceptable standards to properly prevent internal erosion throughthe underdrainage system.

b. Adequacy of Information. Lack of stability and seepageanalyses, including seismic stability and liquefaction studies, is adeficiency which should be corrected, especially in light of' theembankment materials and depositional method.

c. Urgency. Remedial measures should be initiated promptly onthe deficiencies described herein.

d. Need for Phase II. No Phase II investigation isrecommended. Action should be initiated on the measures proposedherein.

7.2 REMEDIAL MEASURES.

The following remedial measures are recommended:

a. The hydraulic capability of this dam should be increased tosafely hold and/or pass a flood of PMF magnitude. This should beaccomplished under the direction of an engineer experienced in thedesign and construction of dams. It should be noted that additionalreservoir filling due to tailings disposal will alter therelationships of storm inflow, reservoir storage, and requiredspillway outflow.

b. The potential for failure due to internal erosionassociated with the crushed rock and pipe drains should beminimized. Provisions for reducing this susceptibility through theuse of graded filters and/or drains designed according to currentlyacceptable standards should be made.

c. In conjunction with item "b" above, a regular monitoringand inspection program should be instituted to provide for earlydetection of internal erosion should it occur, whether from drainagefeatures or elsewhere on the embankment and abutments. Seepageflows should be closely monitored for changes in volume/rate, amountof transported sediment, and water quality characteristics.

20

d. A contingency program of remedial efforts to be institutedif internal erosion or other failure evidence becomes apparentshould be formulated. This program should be maintained with allappropriate company personnel and civil officials aware of itsprovisions.

e. Tailings disposal should be planned to prevent a free poolsurface from resting against the upstream face or the dam embankmentas explained in Section 3.2.

f. Maintenance on a regular basis is recommended to repairsurface erosion features, expecially those at the abutment contacts.

g. The dam should be periodically inspected by an experiencedengineer and records kept of all inspections and maintenance efforts.

h. Stability and seepage analyses, including seismic stabilityand liquefaction studies, should be performed by a professionalengineer experienced in the design and construction of dams.Additionally, a stability analysis of the abutment slope locatedabove the spillway should be performed with due consideration givento potential erosion within the spillway at the slope toe.

21

Appendix A

HYDROLOGIC AND HYDRAULIC ANALYSIS

1. The hydrolorin analysis used in development of the overtoppingpotential is based on applying a hypothetical storm to a unithydrograph to obtain the Inflow hydro7raph for a reservoir routing.The Probable Maximum Precipitation is derived and determined fromregional charts prepared by the National Weather Service in"Hydrometeorological Report No. 33." Reduction factors have notbeen applied. A 24-hour storm duration is assumed with total depthdistributed over 6-hour periods in accordance with proceduresoutlined in EM 1110-2-1411 (SPD Determination). The maximum 6-hourrainfall period is then distributed to hourly increments by the samecriteria. Within-the-hour distribution is based upon NOAA TechnicalMemorandum NWS HYDRO-35. The non-peak 6-hour rainfall periods aredistributed uniformly. All distributed values are arranged in acritical sequence by the SPF criteria. The final inflow hydrographis produced by deduction of infiltration losses appropriate to thesoil, land use, and antecedcnt moisture conditions.

2. The reservoir routing is accomplished by using Modified Pulsrouting techniques wherein the flood hydrograph is routed throughlake storage. The hydraulic capacity of the spillway is used as anoutlet control in the routing. Storage in the pool area is definedby an elevation-storage capacity curve. The hydraulic capacity ofthe spillway is defined by an elevation-discharge curve. Thestorage routing effect of the upper reservoir is included in theanalysis.

3. Dam overtopping analysis has been conducted by hydrologicmethods for this dam and lake. This computation determines thepercentage of the PMF hydrograoh that the reservoir can containwithout the dam being effectively overtopped. An output summary inthis hydrologic appendix displays this information as well as othercharacteristics of the simulated dam overtopping.

4. The above methodology has been accomplished for this reportusing the systemized computer program HEC-1 (Dam Safety Version),July 1978, prepared by the Hydrologic Engineering Center, U.S. ArmyCorps of Engineers, Davis, California. The numeric parametersestimated for this site are listed on PLATE A-5. Definitions ofthese variables are contained in the "User's Manual" for thecomputer program.

5. The spillway rating curve for the upper reservoir was computedusing the methods of "Hydraulic Charts for the Selection of HighwayCulverts," Hydraulic Engineering Circular #5, Bureau of PublicRoads, Department of Commerce, GPO, 1965. The spillway rating curvefor the open channel of the main tailings dam was developed using

22

, 'I:

the step backwater computations of computer program HEC-2, datedAugust 1977. Copies of the input data and output from HEC-2 areattached as pages A-i to A-4.

6. The attached pages A-I4 through A-22 are copies of input andoutput data for the overtopping analysis. Since this dam preventsthe effects of overtopping primarily by runoff storage, anantecedent storm of the magnitude of 25 percent and 50 percent ofr the PMF was considered to have occurred prior to the 50 percent PM?and 100 percent PM? storms, respectively, and appropriate storage is

included in the starting elevation prior to reservoir routing.

23

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APPENDIX B

Engineering Data and Plates Furnished by the Owner

-~~~ +~;.-iI

L77%-2t

ii! t:! A

.ii~WE

I-iP

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FT

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t- t--_--TI? =77__

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______________________________________________

II -. 5

5. I

NOTES:I Piezometers art, opn-s: ; ter,~.2. Piezometer:; do !iot I fe on~ a s' aiit Wry:w 1,e

Plan locations ar, M ': PLATE B-.3. Piezorneter read :n.:s a * aim e: :-, i-on"t

early 1974.4. Piezometer 2 las! tIirt t s 0: ''- ~ d. ae : t

hatch-:nark at el~vat it) !," Vic sr w, i ea;cr wtrotnd Q I e'at Ior wflt f~ *izk .. was a!)D-ox" a! V s.three reaW: o r.t

KK

:..co ' c, st w O'M$00

100-7

1+0 24oo 30 e0 +CO0

piezo:-!, cr is no: Tho , ; i L was 'ev'ro-,e..!

tv c ha;-,krcnf .. '. reci;.i i 'or Piezom( er I. are ~ Iv la;,le .

Po -:Cca i w* ,

t2~i I)'Ve

119i~o

4? 00 1130~ea~2O

t itn lot RC O h14o' r edns

PLAT1S0

R R R a st L

rr I 1

"02m~

-) ON

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U aw cu

cs ~ ~ W W

a )0) 'z

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( .

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) /

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) 'I

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ii- 'I

* *.. . . - ( I 'I --

btt

%~ X!: -74 .r

PHOTO 1: Dow~nstream slope at uncompleted portionof emibankment. Spillway is in background.

, T.

,PHOTO 2: Downstream slope from embankment crest.Flags indicate piezometer locationsSeepage reclamation pond is in background.

44

PITO 3: Downstream slope looking toward southeast(left) abutment.

7-1.

PHOTO 4: Upstream slope during deposition of unse-gregated tailings.

.--r. - 2% -",~~ ~ .. ..'.".-.

PHOTO 5: Upstream slope with scarp created by erosion dueto hydraulic method of tailings deposition

PHOTO 6: Upstream slope and tailings impoundment.

*~.-'A

PiHOTO 7: Upstream slope at uncompleted portion ofembankmnent. Spillway entrance is in background

~~77

'AA

PHOTO 8: Spillway looking downstream.